Solar Cell Busbar: 3BB, 4BB, 5BB Comparison
In modern solar cell design technology, there’re 3 main types of busbars: 3BB, 4BB, and 5BB. These figures represent the number of metalized strips a single solar cell has printed on the front and rear sides.
The number of busbars a solar cell has affects some parameters such as resistance losses, shading losses, residual stresses, efficiency, and overall performance.
In this article, we’ll compare 3BB, 4BB, and 5BB solar DC bus bars and hopefully help you know the best busbar type that’s worth your money.
But before we analyze each of these multi-busbar solar modules, let’s first discuss what busbars are and their role in solar cells.
What is a Solar Cell Busbar?
A solar cell busbar is a thin metallic strip printed on both sides of a solar cell. These metallic strips are printed on the front and rear sides of a solar cell.
In solar panel designs, solar busbars are contained in busways or protective coverings. With this design, DC transmission points can be created anywhere on the modules.
Solar cell bus bars are flat strips with a high surface area to cross-sectional area ratio. This design modification aids inefficient heat dissipation, thus maintaining optimum power production efficiency of the solar modules.
The Role of Busbars in Solar Panels
Solar busbars have one crucial role:
To conduct DC power produced by the solar cells on being hit by light photons to the solar inverter.
The solar inverter then converts DC power to AC power.
In light of the conductivity role, solar busbars are usually made by a material of high conductivity.
Here’s a closer look at how solar busbars are added to solar cells.
How Busbars are installed on Solar Cells?
Screen printing technology is used to add these contact strips to the rear and front sides of a solar cell.
Screen printing involves depositing the busbar material–usually a paste– on the substrate (solar cell) using a strip screen.
In most solar cells, the busbars are made of a silver paste.
With silver as the build materials, the busbars can be manipulated to improve conductivity on the front side and reduce oxidation on the backside.
Other conductive materials can also be used as busbars, but we’ll discuss more on that later.
For now, let’s explore the components that work hand in hand with solar busbars enabling them to perform their power transfer role.
Integral Solar Busbar Components
There’re 3 main complementary components needed for solar busbars to perform their role efficiently: grid fingers, string/tab wires, and insulation.
Let’s look into each of these components briefly.
Grid fingers are the interconnections between busbars. These extra thin interconnecting strips are usually perpendicular to the busbars, and their role is to collect current produced by the solar cells and deliver it to busbars for conduction.
Grid fingers have no definite numbers, but they vary depending on the space left between solar busbars.
This is the string of wires that connect busbars, thus interconnecting the cells in the solar module setup.
The current from every solar cell’s busbar is collected by the string wires and joined into one spot.
Usually, the endpoint of these wires is the junction box. This is the point where all the produced DC power exits a solar module.
Insulation prevents energy losses from a solar module. An insulation material helps keep the yield of a solar cell at a maximum.
Busbars are either insulated with the support structures or entirely around them.
With this knowledge, it’s now easier to understand what solar cell busbar numbers 3, 4, and 5 mean.
How many Busbars Should a Solar Cell have?
In solar cell manufacturing, determining the number of busbars a solar cell should have is a significant design consideration. This is because the number of solar busbars directly affects the solar cell’s efficiency and ultimately how a solar panel performs.
The old solar cell design technology limited the number of busbars in a single solar cell to 2 busbars (2BB).
Thanks to technological advancement, solar cells now have 3 busbars (3BB), 4 busbars (4BB), and 5 busbars (5BB).
Generally, the number of busbars affects resistance losses and shading losses in distinct ways.
Resistance losses are caused by the increased distance between two metal contacts. This is definitely a characteristic of solar cells with a low number of busbars.
On the other hand, shading losses are caused by having too many metal contacts on one solar cell, thus barring light from hitting the solar cells (shading). This feature characterizes solar cells with a high number of solar busbars.
To help you understand this effect, we’ll compare modern busbar numbers: 3BB, 4BB, and 5BB under the following factors:
- Power production efficiency
- Cost on the consumers’ end
- Manufacturers cost
- Fill factor
- Degradation rate
The more bus bars a solar cell has, the shorter the distance the direct current travels from its point of production.
This simply means that the speed of current transfer is high, which in turn translates to enhanced efficiency.
So, if you have a solar panel with 5BB, it’ll be more power-efficient than a bus bar with 3BB or 4BB.
Note that even the slightest increase in efficiency can make a huge difference in the module’s performance. In fact, this effect led to the introduction of busbarless solar cells, which we’ll discuss later in this guide.
Solar panels are sold following the Watt Peak (WP) rating. So, if the power rating of 3BB, 4BB, and 5BB solar panels is the same, their overall price will be roughly the same.
However, considering that efficiency improves with the increasing number of bus bars, buying the 5BB modules is more economically viable than buying the 3BB or 4BB modules.
Please note: The power rating is not the only factor that affects the price of solar cells. Other factors such as the amount and type of busbar material used also affect the cost of solar cells. For example, since a 4BB solar cell uses more plating material than a 3BB, it’ll end up costing more.
Here are some price estimates you should expect to pay for 3BB, 4BB, and 5BB solar cells.
- 3BB-$0.11-$0.14 per piece
- 4BB-$0.13-$0.16per piece
- 5BB-$0.20-$0.45 per piece
The cost of manufacturing 5BB solar cells is higher than that of manufacturing 3BB and 4BB solar cells. This is because more of the plating material is needed when a solar cell is printed with more busbars.
In addition, more advanced equipment is needed to print more bus bars on a single solar cell.
While this cost is insignificant on the consumer’s end, it’s quite capital intensive for manufacturers.
The fill factor of a solar cell is its power production quality.
This parameter is calculated by comparing power produced by the solar cells with the expected theoretical power.
Obviously, since the efficiency of solar cells increases with increasing busbars, the fill factor of solar cells also increases from 3BB to 4BB to 5BB.
Printing the conductive metallic strips and soldering wire strings on solar cells causes residual stress. Over time, this residual stress turns to micro-cracks that, in turn, increase the degradation rate of solar modules.
In line with this effect, you may conclude that 5BB solar cells have a higher degradation rate than the 4BB and 3BB solar cells. But this is not the case.
The higher busbar solar cells have a shorter distance between the metallic strips; hence the residual stresses and degradation rates are lower.
Current Solar Cells Busbar Trends
Solar cell busbar production technology is changing day in day out— manufacturers aim at not only increasing the efficiency of solar cells but also cutting the cost of busbar production.
Other than busbarless solar cells, the other popular busbar design trends include:
Replacing silver with less costly conductor materials
Instead of relying on silver which is quite expensive, solar manufacturers are going for materials such as copper, tin, or nickel.
These materials are as good as silver in terms of electrical conductivity but cost a fraction of what silver costs.
Swapping full-line silver metallization for dash-line designs
Dash-line busbar designs reduce material usage and definitely the cost of production. A single solar cell can have up to 8 dash lines, but this is still less material-consuming than a 3BB line solar cell.
Please note: Every emerging busbar design trend has its own limitations.
For example, the dash-line busbar design is prone to micro-cracks that compromise the quality and production capacity of solar cells.
So, optimization is still needed in solar busbar production technologies to render them fully effective in solar power production.
Is the number of busbars the only factor that affects the performance of solar cells?
Should you invest in 3BB, 4BB, or 5BB Modules?
The more bus bars your solar panels have, the better the power production efficiency.
Also, regardless of shading losses, 4BB and 5BB solar cells have a comparative advantage over 2BB and 3BB solar cells– their overall efficiency and performance are higher.
In a nutshell, the higher the number of busbars in a solar cell, the more reliable the solar cell is in producing DC power, hence the more value you’ll have for your money.
Must a Solar Cell have a Busbar?
For a long time, we’ve seen manufacturers focus on solar cells with busbars and string wires. However, there’s a new trend where solar cells are produced busbarless.
Busbarless solar cells are the exact opposite of multi-busbar solar cells. They have no conducting metallic strips both on the rear and back sides.
The main aim of this design approach is to increase the power production to space ratio of solar cells.
This is a result of reduced shading, which is a common problem with multi busbar solar cells. Additionally, busbarless solar cells have reduced localized defects such as micro cracks.
Lastly, busbarless designs save on the material costs needed to build the busbars.
Is the number of busbars the only factor that affects the performance of solar cells?
The number of solar busbars is the main factor that affects how solar cells perform, but not the only one.
Solar module manufacturers have to strategize on other parameters such as quality of the busbar materials, solar cell busbar width and height, width and height of grid fingers, and the space between the grid fingers when optimizing solar cells.
Does the size of busbars impact solar cell performance?
The size of the busbar determines the amount of current that the solar module can conduct. So, the larger the busbars, the more current they conduct.
What are battery busbars?
A battery busbar is a point of connection where all the loads to a battery setup are directed.
Since the battery busbar is usually a long metalized strip, the load is spread better across the battery bank; hence your batteries last longer.
Unlike in solar cells where the busbar is a long flat strip, a battery busbar is an actual ‘metallic bar’ with connection points. The biggest advantage of solar battery busbars is that they increase the longevity of your battery bank.
So, if you have a 48V solar rechargeable battery setup, you should consider investing in a battery busbar.
There you have it. Now you know what sets apart 3BB, 4BB, and 5BB solar busbars and, more importantly, how the number of busbars affects your solar module’s production efficiency.
From an investment point of view, staking your money on a 5BB solar module is more worthy than purchasing a 3BB or 4BB for the same wattage rating.
While in this post we limited our discussion to 3BB, 4BB, and 5BB solar cell busbars, you should expect to see more and better busbar designs, especially now that solar technology is moving towards increasing the efficiency of PV modules while reducing the overall cost.
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